Anti-cavitation system in pipelines which avoids that the fluid reaches its vapour pressure at the output of a given contraction using a device that connects the output section of the contraction with its downstream pressure

ABSTRACT

A anticavitation system that has a pipeline piece ( 1 ) that has a contraction ( 3 ), as an example a valve. Upstream of the contraction ( 3 ) the fluid moves in a direction ( 2 ) with a P 1 , and downstream of the contraction ( 3 ) with a pressure P 2 . To avoid that the fluid pressure reached the Pv, exiting the contraction ( 3 ), the system has cavities and holes ( 4 ) located downstream of the contraction, where the pressure is stable and reaches a value P 2 . The system has a second set of cavities ( 5 ) located just outside the contraction ( 3 ). Using a connection media ( 6 ) the system feeds back the stable prssure P 2 , to the area outside the contraction ( 3 ) where the pressure reaches Pv and can produce the undesirable cavitation. For this, as it feeds back the pressure P 2  using the connection media ( 6 ) to the cavity ( 5 ), the pressure exiting the contraction ( 3 ) reaches a value P 3  that is higher than Pv. The connection media ( 6 ) can have a chamber-chamber ( 9 ) that has a surrounding ( 7 ) and the external wall of the pipeline ( 1 )

FIELD OF APPLICATION OF THE INVENTION

The invention mentioned in this document refers to a new device thatallows to suppress the phenomenon called cavitation that affects controlvalves in industrial processes with a higher efficiency than with thecurrent systems and mechanisms and from a different approach.

CAVITATION DESCRIPTION

Cavitation is a multi-step phenomenon that occurs in a liquid flowstream. First, due to some changes in flow geometry (such as a valve),the fluid falls below its vapour pressure, which creates some vapour inthe liquid.

Next, the fluid returns to a pressure that is greater than its vapourpressure, causing the vapour bubbles to collapse. The formation andcollapse of vapour bubbles is referred as cavitation.

To better understand the phenomenon of cavitation, one can start byanalyzing the velocity and pressure profiles of a fluid as it passesthrough a restriction.

The important point to note is that at the smallest cross-sectional flowarea of the fluid stream (referred to as the Vena Contracta), fluidvelocity increases and the fluid pressure decreases. This relationshipbetween fluid velocity and fluid pressure is known as Bernouilli's Law.

1. As fluid flows through a restriction, fluid velocity increases

2. Bernouilli's Las: If velocity increases, pressure will decrease.

3. The Vena Contracta, downstream of the restriction, is the point ofsmallest flow area, highest velocity, and lowest pressure.

If the pressure of a liquid falls below its vapour pressure, the liquidwill begin to vapourize. If the vena contracta pressure (Pvc) fallsbelow the vapour pressure (Pv) of the fluid, then fluid vapourizationwill occur.

If the downstream pressure P2 increases to a value that is greater thanthe fluid's vapour pressure, the bubbles collapse and the fluid iscavitating.

If the vapour bubbles that are formed during the cavitation cycleimplode on or near fluid boundaries such as valve components and pipewalls, high velocity microjets and sonic waves can result in rapid andserious damage to the components of the valve and pipeline.

COMMENTS REGARDING PRIOR ART

Document U.S. Pat. No. 3,946,562 (Ross) of Mar. 30^(th), 1976 shows acavitation suppressor to be used on hydraulic systems. The CavitationSuppressor is useful to prevent the excessive pressure using a hydraulicfluid bypass around a mix section to reduce the use of additional fluidaspiration from a reservoir.

The Cavitation Suppressor prevents the incorporation of air within thesystem from the added solution. It includes and input, a mixer andoutput sections, additionally to the bypass media which communicates theinput and output sections.

Document U.S. Pat. No. 4,016,898 (Tokarchuk et al.) of Apr. 12^(th),1977 show a cavitation and bubble suppressor in a fluid passing througha high pressure relief valve, where that fluid is coming from a valvewith high counter pressure on the discharge line of the relief valve.The high-pressure valve has pistons with differential area which keepsthe counter pressure on a fixed rate with respect to the high pressureuntil reaching the relief valve's input. This rate is at least 1:3.

Document U.S. Pat. No. 4,739,794 (Ballum) of Apr. 26^(th), 1988 show ananticavitation configuration for a rotary valve that includes a bypassconduit on the flow passage that connects the upstream and downstreamterminals of the valve's passage. A manual valve is placed in theconduit and it is open to measure a vacuum over the flux terminaldownstream of the valve or by manual mechanisms to allow the processfluid to freely flow to the vacuum and, by that way, prevent cavitation.

Many documents about the previous art are using a bypass whichcommunicates the fluid's pressure downstream and upstream of thecontraction or valve, where additional devices or connections are neededto avoid cavitation, increasing the total cost of the solution.

BRIEF SUMMARY OF THE DRAWINGS

The attached drawings, that are included in order to provide a betterunderstanding of the invention, illustrate part of the previous art andan execution of the invention, along with the description, allows toexplain the principles of the invention.

FIG. 1 shows the cavitation effect, that is produced at the exit of acontraction of the pipeline, when the fluid gets to a value below Pv.

FIG. 2 shows the schematic of the theory of the solution proposed by theinvention, that also comes with a pressure graph.

FIG. 3 shows the product.

FIG. 4 shows the product in a different angle

FIG. 5 shows the product from a different angle

FIG. 6 shows the pipeline without the invention

FIG. 7 shows the pipeline with the invented product.

DESCRIPTION OF THE INVENTION

The anticavitation system consists of a piece of pipeline (1) of acompatible material to the fluid to handle corrosion, erosion, pressure,or temperature; This material can be Carbon Steel, Stainless steel 316SST, 304 SST, 321 SST, Hastelloy C275, Avesta 254 smo, plastics HDPE,CPVC, etc

The schedule can vary from SCH 40 to SCH 160. The length of the pipeline(1) is designed case by case to be adopt the existing pipeline or inprojects that have specific operating process conditions of flow andpressure.

The anticativation system consists also of a series of cavities (5)between the pipeline (1) that are connected using feedback of the sameprocess fluid that is located downstream of the valve (3) in an areawhere P2 has stabilized, in order to provide pressure to the venacontracta to a value Pv.

The anticavitation system has a pipeline (1) that has a contraction (3),for example a control valve. Upstream of the contraction (3) a fluidthat moves in a direction (2) that has a pressure P1, and downstream ofthe contraction (3), the fluid has a pressure P2. To avoid that thefluid pressure decreases to its steam pressure Pv, immediately aftercontraction (3), the system has a cavity (4) that is located downstreamof the contraction, where the pressure is stable and gets to a value P2.The system has a second cavity (5) located immediately downstream of thecontraction (3). Through a connection (6) the system feeds back with thestable pressure P2 to the area immediately downstream of the contraction(3) where the pressure can decrease to Pv producing a potentialcavitation. Therefore, with the connection (6), the output pressure ofthe contraction (3) increases to a value P3, where this value P3 ishigher than the steam pressure Pv and less than P2.

FIG. 3 shows the preferred model for this invention, where the producthas a pipeline piece (1). In this case, te contraction (3) is not shownin FIG. 3, but it can be any type of valve, and therefore this productcan be connected downstream of the valve. In the preferred model of thisinvention, teh cavity (4) that is downstream of the valve (3), has holeswhere the pressure is stable and takes a value P2. The product has asecond group of cavities (5) could be also holes, that are locatedimmediately in the exit of the contraction or vlave (3). The connectionpiece (6) that feed the pressure stable P2, to the area exiting thevalve (3) where the pressure can reach Pv, is a space (9) composed of asurrounding (7) and the external wall of the pipeline (1), that allowsthe communication of the holes (4,5). This way this space allowing thatthe pressure that is above the holes (4), can be feeded to the exit ofthe valve (3), and this way allowing to reach a value P3, where thisvalue P3 is higher than the Pv and lower than P2 downstream of the valve93). This product can be attached to any kind of pipeline configuration,where the preferred connection (8).

FIGS. 6 and 7 shows the invention product, that can be built with apipeline piece (1) that can be made holes in its ends, to get thecavities (4,5), and then is mounted to the surrounding (7) to make thechamber space (9)—connection (6)—where the ends can be added endconnections (8) to simplify the mounting at the exit of the valve (3).

This system allows the following advantages:

-   -   The current systems of the previous art, such as cavitation        attenuators, produce high additional pressure losses, reducing        the flow capacity of the valve. This invention product shall be        minimal, as it does not consider additional pieces inside the        valve that could be in contact with the fluid.    -   Aspiration tubes present limitations to work with corrosive,        toxic, or explosive fluids, as there are always probabilities to        spill the product through the check valves. Our system considers        using the same proces fluid to pressurize the vena contracta        area, therefore it does not need to inject or add external        fluids that need check or cut valves to control the fluid that        pressurizes the vena contracts.    -   Additionally this system does not have fluid losses or spills.

1. An anticavitation system for a pipeline having a contraction, whereupstream of the contraction the fluid has a pressure P1, and downstreama pressure P2, comprising: a first cavity downstream of the contractionwhere the pressure is stable and has a value P2; a second cavity locatedimmediately downstream of the contraction; a connection deviceconnecting the first cavity with the second cavity and feeds back thestable pressure P2, to the contraction area.
 2. A system; according toclaim 1, characterized in that the pressure outside the contractionreaches a value P3 that is less than P2.
 3. A system according to claim1, characterized in that contraction is a valve.
 4. A system, accordingto claim 1 characterized in that the first cavity is a group of holes.5. A system according to claim 1 characterized in that the second cavityis a group of holes.
 6. A system according to claim 1 characterized inthat the connection media comprises a chamber having a surrounding andthe external wall of the pipeline.
 7. A system according to claim 1characterized in that the system has in its extremes flanges forconnection to any kind of pipeline installation that has fluid.
 8. Asystem according to claim 1 characterized in that the pipeline materialis compatible with the characteristics of the fluid.
 9. A systemaccording claim 1, characterized in that the pressure exiting thecontraction reaches a value P3, where this value P3 is higher than Pv.10. A system according to claim 1 wherein the characteristics of thefluid is at least one selected from corrosion, erosion, pressure, andtemperature,
 11. A system according to claim 1 wherein the pipelinematerial comprises Carbon Steel, Stainless Steel 316 SST, 304 SST, 321SST, Hastelloy C275, Avesta 254 smo, plastics HDPE, or CPVC.